This invention relates to a method and apparatus for determining predetermined characteristics of a reel-to-reel recording tape, such as the total overall recording capacity of that tape, and also for determining the remaining recording capacity of that tape even if an unknown quantity of tape already has been transported from its supply reel to its take-up reel.
In many types of recording/reproducing devices, such as video tape recorders (VTR's), audio tape recorders, and the like, various types of recording tapes can be used therewith. Typically, such tapes are housed within a cartridge and are transported, during a recording/reproducing operation, from a supply reel to a take-up reel. Usually, when a tape cassette first is loaded onto the recording/reproducing device, the user is cognizant of the overall recording capacity of that tape (e.g. thirty minutes, one hour, two hours, three hours, and the like), and often the tape is fully rewound onto its supply reel before using. As recording/reproducing proceeds, an indicator, such as a digital counter, provides an indication as to the amount of tape which has been transported to the take-up reel or, alternatively, the amount of tape which remains on the supply reel. These indications provide the user with useful information, for example, as to whether there is sufficient tape remaining to complete the desired recording operation.
There are, however, instances wherein an unknown tape cassette is loaded onto the recording/reproducing device. If the user wishes to know the type of cassette which has been loaded into the device, that is, if the user wishes to know the total overall recording capacity of that cassette, it is necessary to unload the cassette from the recording/reproducing device. In some applications, it may be preferred not to unload the cassette, determine its type and then re-load the cassette back into the device. For example, in a VTR of the type which withdraws a length of tape from the cassette and deploys that withdrawn tape about a recording drum, the exact location of the tape which is positioned for recording may not be the same following the re-load operation as was previously positioned. This may be particularly detrimental during an edit operation.
Furthermore, if a tape cassette that has been partially used, that is, some amount of tape already has been used for recording/reproducing, is loaded into the device, an accurate indication of the amount of tape remaining on the supply reel, or the amount that already has been wound upon the take-up reel, cannot be readily obtained. It may be necessary first to rewind the tape completely to its initial, start position, and then to advance the tape to the location at which it had been loaded into the device. The usual digital counter, if reset after the tape had been fully rewound, then will indicate either the amount of tape which remains for recording or the amount of tape which has been used. It is appreciated that this is a time-consuming and annoying task. Nevertheless, it often is the only technique by which a user can be apprised of the amount of tape which remains for recording.
It has been proposed, in copending application Ser. No. 963,319, to indicate the amount of tape which remains on a supply reel in a cassette used in a VTR, even if an unknown quantity of tape already has been used. However, in this proposal, the determination of the amount of remaining tape is based upon sensing the angular velocity of the supply reel as that reel rotates when tape is withdrawn from the cassette and loaded onto the VTR recording apparatus. During this tape-loading operation, which is to be distinguished from a tape transporting operation wherein tape is driven from the supply reel to the take-up reel, the take-up reel is held stationary. Also, in this proposed technique, there is no suggestion of determining automatically the type of cassette which is used, that is, the total overall recording capacity of that cassette.